Good morning everyone and welcome to episode number 10 of the

physician assistant boards dot-com podcast. I had a question from one of the

listeners regarding dyspnea and how to approach someone when they present to you with shortness of

breath. How do we know if this is a cardiac or a pulmonary problem? What are some

signs, symptoms, or labs that we can use to help differentiate the possible causes.

I figured that if one person had this question many of you would also be interested.

So before we get started, let's go over some simple physiology

first. Now the main muscle involved with inspiration is the diaphragm. The

diaphragm is innervated by the phrenic nerves which are C3c4 and C5. When the diaphrags, this will cause a negative

pressure within the thorax which will draw in air.

The active expiration is passive.

However, the internal and external intercostal muscles are used for forceful expiration. Now there has to be a balance between inhalation

of oxygen and exhalation of carbon dioxide. Once the oxygen is inhaled, it travels down to the alveoli where oxygen and carbon dioxide are

exchanged.

Oxygen is then transported throughout our bodies using chemoglobin.

There are also two chemoreceptors in charge.

You have the peripheral and the central.

The peripheral chemoreceptors are located in the carotids and the aorta and they're in charge of

sensing partial pressure of oxygen. The central chemo receptors are located in

the medulla and sense changes in carbon dioxide. Now when there's an increase in

carbon dioxide this signals the medulla to increase the rate of

respiration in an attempt to expel as much carbon dioxide as possible.

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